A positively or negatively charged atom or (covalently bonded) group of atoms(a molecular ion)

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3. Atomic Masses

3. Atomic Masses

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Realtive Isotopic Mass

The mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12

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Relative Atomic Mass, Ar

The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12

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Relative Molecular Mass, Mr

The weighted mean mass of a molecule compared with one-twelfth of the mass of an atom of caron-12

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Relative Formula Mass

The weighted mean mass of a formula unit compared with one-twelfth of the mass of an atom of carbon-12

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4. Amount of Substance

4. Amount of Substance

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Amount of Substance

The quantity whose unit is the mole. Chemists use 'amount of substance' as a means of counting atoms.

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Avogadro Constant, NA

The number of atoms per mole of the carbon-12 isotope (6.02 x 10 23 mol-1)

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Mole

The amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope.

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Molar Mass, Mr

The mass per mole of a substance. The units of molar mass are gmol-1

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5. Types of Formula

5. Types of Formula

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Emprical Formula

The simplest whole number ratio of atoms of each element present in a compound

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Molecule

A small group of atoms held together by covalent bonds

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Molecular Formula

The actual number of atoms of each element present in a molecule

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6. Moles and Gas Volumes

6. Moles and Gas Volumes

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Molar Volume

The volume per mole of gas. The units of molar volume are dm3mol-1. At room temperature and pressure the molar volume is approximately 24.0dm3 mol-1

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7. Moles and Solutions

7.Moles and Solutions

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Concentration

The amount of solute, in mol, dissolved per 1dm3 (1000 cm3) of solution

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Standard Solution

A solution of a known concentration. These are usually used in titrations to determine unknown information about another substance.

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8. Chemical Equations

8. Chemical Equations

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Species

Any type of particle that takes part in a chemical reaction.

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9. Moles and Reactions

9. Moles and Reactions

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Stoichiometry

The molar relationship between the relative quantitites of sunstances taking part in a reaction

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10. Acids and Bases

10. Acids and Bases

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Acid

A species that is a proton donor.

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Base

A species that is a proton acceptor

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Alkali

A type of base that dissolves in water forming hydroxide ions. OH-(aq) ions.

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11. Salts

11. Salts

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Salt

Any chemical compound formed from an acid when a H+ ion from the acid has been replaced by a metal ion, or another positive ion, such as the ammonium ion NH4+

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Cation

Positively charged ion

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Anion

A negatively charged ion

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12. Water of Crystallisation

12. Water of Crystallisation

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Hydrated

Refers to a crystalline compound containing water molecules

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Anhyrdous

A substance that contains no water molecules

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Water of Crystallisation

Water molecules that form an essential part of the crystalline structure of a compound.

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14. Oxidation Number

14. Oxidation Number

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Oxidation Number

A measure of the number of electrons that an atom uses to bond with atoms of another element; they are derivied from a set of rules.

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15. Redox Reactions

15. Redox Reactions

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Oxidation

The loss of electrons or an increase in oxidation number.

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Reduction

The gain of electrons or a decrease in oxidation number.

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OILRIG

Oxidation Is Loss Reduction Is Gain

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Redox Reaction

Reaction in which both reduction and oxidation take place.

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Reducing Agent

Reagent that reduces (adds electrons to) another species.

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Oxidising Agent

Reagent that oxidises (takes electrons from) another species

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Unit One-Atoms, Bonds and Groups

Module 2- Electrons, Bonding and Structure

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1. Evidence for Shells

1. Evidence for Shells

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First Ionisation Energy

The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

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Electron Shielding

The repulsion between electrons in different inner shells. Shielding reduces the net attractive force from the nucleus on the outer shell electrons.

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Successive Ionisation Energies

Measure of the energy required to remove each electron in turn.

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2. Shells and Orbitals

2. Shells and Orbitals

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Shell

Group of atomic orbitals with the same principal quantum number,n. Also known as main energy level.

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Prinicipal Quantum Number,n.

Number representing the relative overall energy of each orbital, which increases with distanced from the nucleus. The sets of orbitals with the same n value are referred to as electron shells or energy levels

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Atomic Orbital

A region within an atom that can hold up to two electrons with opposite spins

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3.Sub-shells and Energy Levels

3. Sub-Shells and Energy Levels

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Sub-Shell

A group of the same type of atomic orbitals (s, p, d and f) within a shell.

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Electron Configuration

The arrangement of electrons in an atom.

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5. An Introduction to Chemical Bonding

5. An Introduction to Chemical Bonding

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Compound

A substance formed from two or more chemically bonded elements in a fixed ratio, usually shown by a chemical formula

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6. Ionic Bonding

6. Ionic Bonding

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Ionic Bond

The electrostatic attraction between oppositely charged ions.

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Giant Ionic Lattice

A three dimensional structure of oppositely charged ions, held together by strong ionic bonds.

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7. Ions and the Periodic Table

7. Ions and the Periodic Table

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Group

A vertical column in the periodic table. Elements in the same group have similar chemical properties and their atoms have the same number of outer shell electrons.

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8. Covalent Bonding

8. Covalent Bonding

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Covalent Bond

A bond formed by a shared pair of electrons.

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Lone Pair

An outer-shell pair of electrons that is not involved in chemical bonding.

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9.Further Covalent Bonding

9. Further Covalent Bonding

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Dative Covalent/Coordinate Bond

A shared pair of electrons which has been provided by one of the bonding atoms only.

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11. Electronegativity and Polarity

11. Electronegativity and Polarity

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Electronegativity

A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond

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Permanent Dipole

A small charge difference across a bond that results from a difference in the electronegativities of the bonded atoms

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Polar Covalent Bond

Has a permanant dipole.

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Polar Molecule

Has an overall dipole when you take into account any dipoles across the bonds.